Study On The Stability Of Organic Carbon Associated With Macro-aggregates In Forest Soils

Forest ecosystem is the largest organic carbon pool in terrestrial ecosystem, playing a vital function in the global carbon cycle. Organic carbon stored in forest soil is mainly occluded into macro-aggregates. Understanding the stability of organic carbon associated with macro-aggregates in forest soils could provide important information in assessing carbon balance in forest and in terrestrial ecosystem. This study aimed at the forest soils collected from 9 sites across a climatic gradient in China. Typical coniferous and broad leaved forest at each site were considered. Soils were sampled from 0-10 cm and 10-20 cm layers.Mineralization of organic carbon and nitrogen in macro-aggregates and their relationship between soil and climatic factors were analyzed. The effects of macro-aggregates destroying and simulated nitrogen deposition on the mineralization of organic carbon in macro-aggregates were also examined in this study. The main conclusions are as follows:1. The cumulative mineralization of organic carbon, potential mineralization of organic carbon and cumulative mineralization of nitrogen associated with macro-aggregates in forest soils decreased with increasing soil depth. The ratio of mineralized carbon to total organic carbon and the ratio of potential mineralized carbon to total organic carbon increased with increasing soil depth. However, soil depth had no significant effect on the mineralization constant of organic carbon.2. The contribution rate of ammonification to mineralization of soil nitrogen was greater than that of nitrification. In general, the mineralized organic carbon and organic nitrogen in broad leaved forest were greater than that in coniferous forest, while the effect of forest types was not significant.3. The constant of first order equation for organic carbon mineralization in macro-aggregates was not affected by content of organic carbon and total nitrogen. However,cumulative mineralization of organic carbon and nitrogen and potential mineralization of organic carbon increased with increasing contents of organic carbon and nitrogen. However,their ratios to total organic carbon or nitrogen decreased with increasing contents of organic carbon and nitrogen.4. The destroying of macro-aggregates structure stimulated the mineralization oforganic carbon associated with macro-aggregates, indicating that the macro-aggregates structure provided physical protection on organic carbon from loss. Simulated nitrogen deposition reduced the mineralization of organic carbon associated with macro-aggregates in forest soils.5. The cumulative and potential mineralization of organic carbon were only significantly affected by mean annual precipitation, while the cumulative mineralization of nitrogen was only affected by mean annual temperature, with a significant negatively correlation with it.Furthermore, the response of organic carbon mineralization to the destruction of aggregates and the simulated nitrogen deposition were not affected by mean annual precipitation and temperature.